The image formation process utilizing photopolymerization involves a chemical sensitization by chain reaction, and the images thus formed are considered to exhibit a highest sensitivity in the nonsilver salt system photography.
The photopolymerization recording system can utilize polymerization, which is a great physical change, and thus can find a wide range of application. Thus, it goes without saying that many studies have been made on the photopolymerization recording system.
The application of the photopolymerization recording system can be roughly divided into two major groups. In one of the two major groups, the physical properties of polymer images themselves (strength, solubility, transmission, water repellency, etc.) are utilized. Examples of such an application include relief, resist, and PS (presensitized) plate. In the other group, polymer images are visualized as media which are then used as color images. Examples of such an application include color proof.
The former application has advantages which are not seen in the silver salt system photography. Despite its low sensitivity, the former application is so advantageous that it has already found various industrial uses.
However, the latter application provides too low a sensitivity, and its use is limited. Therefore, many approaches which comprise the use of silver halide as sensors have been studied.
However, from a different point of view, the color image formation process utilizing photopolymerization is greatly advantageous in that as compared to the silver salt system photography it is free of silver and thus costs less and needs no processing for the removal of silver halide or silver.
Photopolymerization color image recording materials and color image recording methods which can make the best use of these advantages have been studied.
With the exception of special examples (e.g., the case where the monomer itself serves to color as N-vinylcarbazole-carbon tetrabromide light-sensitive materials), it is difficult to directly form visual images by photopolymerization using ordinary photopolymerizable compounds. This is one of the reasons why the photopolymerization system can be hardly applied for the ordinary color image recording process.
In order to visualize images in the photopolymerization recording system, the following physical treatment is needed. In particular, the exposed or unexposed portions are selectively dyed with a dye solution or colored upon being attached to a pigment powder by their difference in permeability or adhesiveness, or a light-sensitive layer which has been previously colored is imagewise exposed to light to form the corresponding polymer image, and the uncured portions are then washed off or peeled off by the use of the difference between the cured portions and the uncured portions in physical properties such as solubility or adhesiveness.
A number of approaches have been proposed for directly visualizing images by chemical reaction in a light-sensitive material comprising a photopolymerizable composition without externally coloring the material or spatially separating the exposed portion from the unexposed portion. In JP-A-52-89915 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"), a method is proposed which comprises the formation of positive-positive visible images by heat development of a photopolymerizable composition and a heat-sensitive coloring material. However, this approach is disadvantageous in that it uses a binary heat-sensitive coloring substance consisting of two components which must be separately positioned inside and outside or on the opposite sides of the photopolymerizable composition.
In JP-A-57-179836, JP-A-57-197538, JP-A-58-23024, and JP-A-58-23025, methods are described which comprise the compression of a photopolymerizable composition and a heat-sensitive (pressure-sensitive) coloring material to form visible images. However, all these methods are disadvantageous in that one of the two components constituting a binary coloring substance must be contained in microcapsules together with the photopolymerizable composition and a pressuring process is needed to destroy uncured capsules.
The above mentioned process which utilizes reaction to form dyes is disadvantageous in that the molecular design of leuco dyes to be used is extremely limited and the dyes thus formed exhibit a poor stability. As described above, the formulations of the composition are complex and subject to various limitations. For example, it is difficult to form a color image of two or more colors. This process is also disadvantageous in that it involves diffusion or transfer which normally deteriorates image sharpness.
Besides these approaches, there have been made many other improvements or approaches. However, these approaches leave to be desired. Further studies are needed to provide a simple, stable and sharp photopolymerizable color image-forming material.
Furthermore, it is difficult to apply the photopolymerization recording system for full-color image-forming material which provides two or more, preferably three or more colors.
To this end, a number of approaches have been developed and put into practical use. For example, a photopolymerizable layer is previously colored with a pigment every single color. After polymerization, the unpolymerized portions are eluted with a solvent. In another process, peeling development is effected to separate the polymerized portions and the unpolymerized portions onto different sheets. In an alternate method, the adhesiveness of the unpolymerized portions is used to adsorb a colored powder. Furthermore, after the unpolymerized portions are washed off, the remaining polymerized portions are dyed. However, these approaches are disadvantageous in that complex steps such as coating, drying, polymerization and processing are needed according to the number of colors required. In addition, precision positioning is required. Thus, the finished color images are obtained in a low yield and at a rather high cost.
In order to minimize the number of sequential steps every single color, some approaches have been proposed. In a process disclosed in JP-A-59-30537, cyan, magenta and yellow color image sheets are exposed to a three color-separated image, and images are then transferred to a development sheet three times to form a full-color image. However, even this process involves tedious exposure and transfer processes. Furthermore, a problem of positioning images cannot be eliminated in this process.
In the photopolymerization color image formation process described in JP-A-62-143044, a material and method which employ only one exposure and one processing to form a full-color image are proposed.
This full-color image-forming material comprises a light-sensitive layer containing three sets of micro-capsules. Each set of microcapsules have distinctly different sensitivities in a selective wavelength range up to the visible spectrum (400 to 700 nm). These microcapsules are combined with cyan, magenta and yellow image-forming agents. These combinations are subjected to pressurization and transfer so that they are allowed to color to form a full-color image.
The expansion of color sensitivity to the visible range is rather significant to the photopolymerization image recording method. However, this microcapusle-coloring process leaves to be desired in image sharpness and stability as described above.
On the other hand, U.S. Pat. No. 3,579,339 proposes another coloring process. In this process, a photopolymerizable composition containing a color coupler of the type used in silver halide color films is bonded to gelatin or the like. The photopolymerizable composition is then coated on a support to prepare a light-sensitive layer containing small light-sensitive polymerizable drops. After exposure, a liquid coloring agent is allowed to penetrate into the unpolymerized oil portions to cause coupling reaction.
Furthermore, JP-A-60-120353 discloses a recording material comprising a combination of an ununiform dispersion of a polymerizable monomer in a binder and a dye to be bleached with the monomer.
These systems are advantageous in that they enable multi-layer coating, and if these monomer oil drops have different sensitivities, a full-color image can be formed at a shot. Furthermore, since these systems involve no physical destruction such as transfer and removal of monomer layer, an easy processing can be effected and a high sharpness can be secured.
However, these dyes produced by coloring reaction or monomer-bleachable dyes are disadvantageous in that the final color images formed of these dyes exhibit a very poor stability. These systems are further disadvantageous in that the degree of freedom of design of dyes having an excellent hue required for color images is very small. Thus, these systems are impractical.
As described above, the photopolymerization color image formation method finds a rather wide range of application. Among these applications, color filters, which have recently found an increasing need, are noteworthy.
In the recent progress of microelectronics, there is an increasing demand for visual data transmission, and various visual apparatus have been developed. Among these visual apparatus, color filters are very significant to provide full-color visual data.
In recent years, small-sized television cameras for home use have employed a solid pickup element such as CCD, BBD and MOS. Such a solid pickup element comprises a large number of finely divided light-receiving portions and a drive circuit for receiving data from the light-receiving portions. In order to obtain color images, a color filter must be positioned on the solid pickup element.
On the other hand, small-sized, thin type and light-weight color displays which can substitute for the conventional color CRT's have been on development. For example, various color display systems utilizing liquid crystal, plasma, fluorescent display tube, electro-luminescence or the like have been proposed.
Among these color display systems, the liquid crystal display system is advantageous in that it can be driven at a low voltage and low power, produced in a thin and light-weight form and has a prolonged life. Thus, the liquid crystal system has come into the limelight. There are various color liquid crystal display systems. Examples of these color liquid crystal display systems include guest-host system (GH system, utilizing a mixture of a binary dye and a liquid crystal), ECB system (electrically controlled bi-refringernce system, utilizing birefringence of liquid crystal), and light shutter system (system utilizing a combination of a liquid crystal cell and a color filter). Among these systems, the light shutter system can correspond to full-color display and is thus considered to be nearest to practical use.
In the light shutter system, the light transmission is controlled by liquid crystal cells in connection with color filters to effect a full-color display. This enables the display of any colors in the color triangle in the CIE chromaticity diagram utilizing the additive process.
The most color filters used to provide a full-color display comprise an array of three primaries (blue, green, red) regularly arranged in mosaic or stripe and optionally have four or more hues. For example, micro color filters for use in solid pickup elements employ black stripes for complete separation of colors between multi-color pattern segments. Also, color filters for use in liquid crystal display often employ black stripes for the purpose of completely separating colors or blocking light to TFT provided in the gap between the above mentioned three primary filters to lower on-current, thereby controlling on-off of light shutter.
As methods for the preparation of color filters there have been known dyeing process, vacuum deposition process, electrodeposition process, interference film process, printing process, and photographic process.
Among these processes, the dyeing process has been most widely used because of its high reliability. In the dyeing process, a polymer such as polyvinyl alcohol and gelatin is coated on a support to form a dye-accepting layer (mordanting layer) on which color elements (pixels) are then formed with a coloring substance such as dye.
Specifically, as described in U.S. Pat. No. 3,289,208, this process normally comprises the steps of: 1) coating a gelatin layer which has become light-sensitive by the addition of potassium bichromate, patternwise exposing the material to light, and washing the material with warm water to form a relief image; 2) dyeing the gelatin left as the relief image with a red dye from a red dye solution; 3) coating an interlayer on the dyed layer; 4) repeating the step 1); 5) dyeing the material with a dyed from a green dye solution; 6) coating interlayer on the dyed layer; 7) repeating the step 1); 8) dyeing the material with a blue dye from a blue dye solution; and 9) coating a protective layer on the material.
However, the dyeing process is disadvantageous in that it requires tedious steps as described above and the color filter thus obtained has a complex structure which is subject to pinhole or flaw.
Many approaches have been proposed to eliminate these disadvantages. For example, U.S. Pat. No. 4,236,098 describes a process which comprises the absorption of dyes by a gelatin layer from a dye solution through window-shaped patterns formed by photoresist technology. In approaches described in U.S. Pat. Nos. 4,081,277 and 4,168,448, heat-sublimable dyes or heat-transferable dyes are transferred to a dye-accepting layer through window-shaped patterns formed of photoresist.
However, these approaches are disadvantageous in that they need to repeat tedious steps such as photoresist coating, development and peeling which result in a poor yield.
Furthermore, in order to eliminate the step of coating a dye barrier interlayer and improve the resistance of dyes in the photoresist process, an approach has been proposed which comprises the use of a pigment-containing photoresist. However, even this process requires steps of coating, drying, exposure and washing every single color and thus leaves to be desired in simplicity and yield.
Other color filter production methods, too, have problems. In the dye vacuum-deposition process, a dye is evaporated and subjected to list-off process to obtain pixels. This process enables a direct formation of such a thin film on a transparent electrode. However, this process is disadvantageous in that the film thus formed exhibits a poor adhesion to the substrate. Color filters comprising an inorganic vacuum-deposited multi-layer interference film exhibit an excellent heat resistance. However, this process is disadvantageous in that the thickness of the interference film can be hardly controlled, causing problems of cost and yield. In the electrodeposition process, a high-molecular weight compound is electrodeposited on an electrode to form a color filter. However, this process is disadvantageous in that it is difficult to make a free arrangement of pixels, making it impossible to make black stripes. The printing process can provide a larger picture and enables mass production as compared to the above mentioned photoresist process. However, this process is disadvantageous in that the film thus formed exhibits a poor dimensional stability, making it impossible to obtain satisfactory properties such as film uniformity and smoothness. Various photographic processes have been studied. However, the conventional photographic processes comprise processing a coupler dispersed in a light-sensitive silver halide emulsion film with a color developing solution to form a nondiffusible dye, and then desilvering the material to form a color filter. Thus, this process is disadvantageous in that it requires tedious processing steps and the color filter thus prepared has a large film thickness and thus exhibits poor properties such as sharpness and hue.
As described above, color filters are very significant for the supply of full-color visual data. However, the conventional color filter production methods require tedious steps which cause a poor yield. Furthermore, color filters thus produced exhibit a poor quality. In particular, it has been keenly desired to provide a process for the preparation of a color filter for large picture with an excellent quality in a simple process.